Such an injection device is disclosed in U.S. Pat. No. 3,882,863 and also, in improved embodiments, in European patent specifications 107874 and 186916. The invention encompasses in addition an injection device for accommodating more than one injection liquid, a plural-compartment injection device, wherein the injection liquids can be injected successively by passing through a suitable by-pass means, e.g. as described in European patent specification 72057.
The above known automatic injection devices or auto-injectors have been developed in particular for use by soldiers in an emergency situation, viz. after having been exposed to a battle gas of the enemy, e.g. a nerve gas. Such injection devices are usually stored for many years at a time (a shelf life of at least 5 years is required by the authorities), after which the device must function reliably at the critical instant. When the injection is required, this must generally be administered through the battle-dress. It will be obvious from the above, that a powerful spring must be used and that, in connection therewith and in relation to the required long storage stability, loaded parts such as the plunger should be manufactured from rigid materials with a high aging resistance, preferably from a suitable metal. In addition, these known auto-injectors are rather complicated due to the great number of cooperating parts, and their friendliness to the user is not fully satisfactory due to their heavy impact after activation.